Although various hypotheses were proposed as to a cause of dental caries in the past, at present, dental caries is recognized as a bacterial infectious disease based on the chemo-microbial theory of Miller. According to the theory, dental caries developmental mechanism is as follows: glucosyltransferase (GTF), which is produced by oral streptococcus, particularly, Streptococcus mutans (hereinafter simply referred to as “S. mutans”), produces sticky and insoluble polysaccharide (glucan) from sucrose in the mouth as a substrate. Bacterial cells of S. mutans adhere onto a tooth surface with the aid of glucan thus produced to form plaque. In the plaque, various microorganisms including S. mutans live together and propagate. An organic acid is produced by metabolism of these microorganisms, acts to reduce the pH within the plaque and decalcifies tooth enamel surface. In this manner dental caries develops and progresses. Furthermore, plaque formation is said to be a cause of not only dental caries but also periodontal disease and bad breath.
As described above, since plaque formed by oral streptococcus primarily including S. mutans is a cause of dental caries, suppressing plaque formation can be eventually an effective means for preventing development of dental caries.
Recently, as a substance having anti-dental caries action, catechins contained in plants have attracted attention. Patent Literature 1 reports that a flavonoid polymer having a molecular weight of 800 to 5000 produced by treating a flavonoid (a catechin) with peroxidase has stronger glucosyltransferase inhibitory action compared to before the treatment.
Non Patent Literature 1 reports that a flavonoid polymer inhibits the activity of glucosyltransferase derived from Streptococcus sobrinus by 50% in an amount of 2.5 μg/mL.
Patent Literature 2 reports that a flavonoid polymer having a molecular weight of 1000 to 10000 and produced by condensing a reduced product of a flavanone/flavanol or a leucocyanidin with a catechin is found to have glucosyltransferase inhibitory activity.
However, these flavonoid polymers are a mixture of flavonoid trimer to pentamer or a mixture of a dimer and a trimer thereof. The compounds contained in the mixture have not yet been isolated. Therefore, the glucosyltransferase inhibitory activity of each of the compounds has not yet been elucidated.
Of the tea daily taken, a mixture of catechins derived from non-fermented tea, i.e., green tea, has been reported to have a glucosyltransferase inhibitory activity (Non Patent Literature 2). However, it has been also reported that a sufficient anti-dental caries action was not obtained in a test using rats.
It has been reported that semi-fermented tea, i.e., oolong tea and their purified products have glucosyltransferase inhibitory activity (Patent Literature 3, Non Patent Literature 3, Non Patent Literature 4 and Non Patent Literature 5). It is also known that glucosyltransferase inhibitory activity is enhanced by treating green tea, oolong tea and black tea with heat (Patent Literature 4) and that glucosyltransferase inhibitory activity is enhanced by treating a catechin with heat (Patent Literature 5).
However, in any case, it has not been elucidated as to which compound in the mixture derived from tea has the activity.